Even though nickel-base superalloys with high strength and strong resistance to chemical attacks at high temperatures are known from the state of the art, for example from EP 1 914 327 A1 and documents cited therein, components made of these materials still need to be protected by corrosion resistant coatings like the so called MCrAlY-coatings, where M stands for iron (Fe) cobalt (Co) or nickel (Ni), Cr stands for chromium, Al stands for aluminium and Y stands for an active element, in particular for yttrium (Y). However, silicon (Si) and/or at least one of the rare earth elements or hafnium (Hf) can be used as the active element in addition to yttrium or as an alternative to yttrium. Furthermore, often thermal barrier coatings are applied onto the corrosion resistant coating in order to reduce the temperature experienced by this coating and the underlying nickel-base superalloy.
There is a trend to increase the temperature of the combustion gases, i.e. the inlet temperature at the turbine entrance, which is related to the aim of increasing the turbine efficiency that in turn depends on the inlet temperature at the turbine entrance. Hence, all parts of a turbine components, i.e. the superalloy of the component and the corrosion resistive coating as well as the thermal barrier coating, need to be improved for allowing the components to operate at higher temperatures.
Moreover, there is a desire not to coat certain areas of turbine blades or vanes, in particular the fixing sections of the blades by which the blades or vanes are fixed to a rotor or a casing. This, however, means that the corrosion resistance of the superalloy itself needs to be sufficiently high.